The present invention relates to equipment for assembly line production of electronic circuit boards, and more particularly, to a computer controlled system for high speed surface mount adhesive placement in circuit board production.
The dispensing of adhesives quickly and reliably in the manufacture of circuit boards on which components are surface mounted is a difficult task. There are inherent speed limitations associated with rotary positive displacement valves, pneumatically actuated syringes and mechanically actuated pinch tubes used in conventional viscous material dispensers. Warped boards, air in the syringe, and stringing of the surface mount adhesive cause inconsistent dispensing and create the need for inspection and rework. As a result, the adhesive dispenser often becomes the bottleneck in the pick-and-place line.
Suppliers in the fluid dispensing industry have been able to make steady incremental improvements in dispensing speed over the past several years to achieve eights dots per second. However, inconsistencies and the need for inspection and rework were not adequately addressed until ASYMTEK of Carlsbad, California developed the DispenseJet (Trademark) apparatus disclosed in allowed U.S. patent application Ser. No. 07/978,783 filed Nov. 19, 1992, issued on Jun. 14, 1994 as U.S. Pat. No. 5,320,250, and entitled METHOD FOR RAPID DISPENSING OF MINUTE QUANTITIES OF VISCOUS MATERIALS. The DispenseJet apparatus uses a nozzle and syringe in combination with a feed tube. The nozzle is impacted by a solenoid actuated hammer to rapidly reduce the volume of a dot generation chamber formed between the nozzle and the feed tube. This causes a jet of viscous material to be ejected from the nozzle and to break away from the nozzle as a result of its own forward momentum. With this new system, it is possible to dispense 72,000 dots per hour from a single head "on the fly" as it passes laterally over a PC board. Adhesive stringing is eliminated with this approach because it does not require wetting of the workpiece surface as is the case with traditional syringe dispenser. The dots generated by the DispenseJet apparatus have a consistent size regardless of height variations in the board due to warpage.
The aforementioned patent application disclosing the DispenseJet apparatus does not disclose the manner in which the apparatus can be supported on a frame and provided with automatic controls for optimum usage in a high volume assembly line.